Various vehicles are provided with an air conditioning system for selectively supplying cool air and warm air to each portion of the interior of the vehicles. During the summer, an air conditioner is operated to supply the cool air, and during the winter, a heater is operated to supply the warm air.
Generally, the heater is operated in a scheme in which a coolant heated while being circulated in an engine and air introduced by a fan are heat-exchanged with each other to supply the warm air to the interior of the vehicle, thereby performing heating. In this heating scheme, heat generated by the engine is used, and thus, energy efficiency is high.
However, during the winter, a predetermined time is required until the engine is heated after starting the vehicle, and then, the heating is not made immediately after starting the vehicle. Therefore, the engine is idled for a predetermined time before being driven until the engine is heated for heating and a temperature of the coolant becomes high, such that problems such as waste of energy and environmental pollution have occurred.
In order to prevent these problems, a method of heating the interior of the vehicle using a separate preheater for a predetermined time in which the engine is heated has been used. A heater using a heating coil according to the related art has a high heat generation amount, such that heating is effectively performed. However, a fire risk is high, and a lifespan of an electric heating wire is short, such that repair and replacement of components are frequently generated, which is inconvenient.
Therefore, a PTC heater, using a positive temperature coefficient (PTC) element, allows the heating to be performed using electric energy of a battery as an auxiliary heating apparatus for heating at the early stage of starting has been used.
The PTC heater may be semi-permanently used due to a low fire risk and a long lifespan. A PTC heater having a relatively small capacity has been mainly used. Recently, a PTC heater having a high capacity has been demanded and developed depending on necessity of users and various kinds of vehicles including an electric vehicle.
A turn on/off of the PTC heater generally controls a capacity in a pulse width modulation (PWM) scheme through a controller.
The PWM scheme, which is one of pulse modulation schemes, indicates a scheme of performing a control by changing a duty ratio of a pulse depending on a magnitude of a modulation signal. That is, the PWM scheme adjusts a control value by adjusting the duty ratio. In this case, the duty ratio of the pulse signal is changed, such that an average value of the pulse signal is changed, and this average value is used as a control signal value.
Korean Patent Laid-Open Publication No. 2010-0078165, published on Jul. 8, 2010, entitled “Air Conditioner for Vehicles and Control Method Thereof” discloses a technology for controlling a heat generation amount of a PTC heater through a control of a PWM signal.
However, at the time of a high voltage PTC heater operation, in the case of the PTC element, noise due to vibrations is generated. Particularly, high frequency noise is generated as an operating frequency becomes higher.
Here, a main noise source is due to vibrations of the PTC element. As shown in FIG. 1, in the case in which the PTC elements 20 are disposed at the same positions in adjacent heat rods 10 to thereby be overlapped with each other, the PTC elements collide with each other by PTC vibrations, such that the noise is increased.
In addition, the noise is increased as a capacity of the PTC heater becomes larger, a size of the PTC heater to a capacity of the PTC heater becomes smaller, or a distance between the heat rods 10 becomes narrower. In this case, the PTC elements generate heat, such that the possibility that the PTC heater will be thermally saturated, and an efficiency of the PTC heater may be decreased.